This application claims the priority of German Application No. 100 41 802.3 filed Aug. 25, 2000, which is incorporated herein by reference.
This invention relates to a compression piston ring provided with a gap region and having cross-sectional changes along the ring circumference which is divided into four imaginary quadrants.
Japanese Published Patent Application 09196171-A discloses a piston ring which has a continuously decreasing wall thickness starting from the ring back and extending towards the ring gap.
A similar piston ring which, however, is composed of two different materials, is described in U.S. Pat. No. 1,278,015. The inner ring region is made of iron or steel and the outer ring region is made of a zinc layer. In this structure too, starting from the ring back, at least the inner part of the piston ring has a decreasing wall thickness extending from the ring back towards the ring gap.
U.S. Pat. No. 2,591,920 describes a piston ring which in the region of its radial end faces or in the region of its inner circumferential surface is provided with circumferential grooves or chamber-like chamfers. The dimension of the grooves or chamfers increases from the ring back towards the gap region.
In practice, in internal-combustion engines compression piston rings of constant wall thickness are widely used. To cause the piston rings to conform to cylinder deformations which may occur, the wall thickness of the piston rings must be reduced as viewed for the entire ring diameter. As a result, if spreading of the ring occurs, the tangential force is reduced or in the presence of a tangential force the extent of ring expansion (spreading) increases. In either case the following problems are encountered:
Insufficient sealing of the combustion chamber;
Difficulties in installing the compression piston ring;
Increased oil consumption;
Increased blowby; and
Ring fracture or ring flutter.
The above-outlined prior art show compression piston rings which also have the above-listed disadvantages as a result of the substantially total reduction of the ring cross section provided over the entire ring circumference.
The manner in which the piston ring is made to conform to the cylinder shape is based on its average shape-conforming capability. In piston rings having a constant wall thickness, a prediction concerning the shape-conforming capability is possible only for a xe2x80x9ctheoretical mid valuexe2x80x9d; the functional behavior of the piston ring, however, is dependent from the worst local conforming possibilities.
It is an object of the invention to provide an improved piston ring of the above-outlined type in which a significantly higher shape-conforming capability in the direction of the gap region is feasible without significantly lowering the tangential force.
This object and others to become apparent as the specification progresses, are accomplished by the invention, according to which, briefly stated, the compression piston ring includes a ring gap defined by facing first and second end faces; a ring back situated diametrically opposite the ring gap; first and fourth quadrants extending from opposite sides of the ring gap and second and third quadrants extending from opposite sides of the ring back to the respective first and fourth quadrants. The first end face is situated in the first quadrant and the second end face is situated in the fourth quadrant.
The wall thickness of the compression piston ring is reduced exclusively in the first and fourth quadrants.
The cross-sectional reduction of the ring wall thickness limited, according to the invention, to the first and fourth quadrants of the ring circumference provides that the ring is capable of better adapting itself to increased cylinder deformations and thus ensures a better sealing of the combustion chamber. At the same time, the shape-conforming capability is increased whereby an overall increased shape-conforming capability for the entire ring circumference is obtained without significantly reducing the tangential force compared to a piston ring having a non-reduced wall thickness.
By virtue of the shape of the cross-sectional reduction in the first and fourth quadrants (which is designed as a function of the mode of application) a purposeful approximation of a predeterminable middle value of the shape-conforming capability of the piston ring may be obtained. The type and configuration of the cross-sectional reduction in the first and fourth quadrants may vary as required, based on the ring cross section and the surface moments of inertia.